metadata: new command to extract and infer metadata from a dataset, given an optional spec file, and create a .metadata file

[jqnatividad]

Now that DCAT-US v3 has reached a recommendation snapshot status -

https://doi-do.github.io/dcat-us/

The metadata command will extract/infer the metadata and save it to a .metadata file.

If a spec file is given, it will use it to inform metadata inferencing (the default spec file will be based on DCAT-US v3 profile).

When uploading to CKAN, the uploader (qsv-pro, DP++) will use the .metadata file to prepopulate metadata fields and set the package to DRAFT mode so the metadata can be curated by the Data Publisher.

The .metadata file will also be used to create an expanded data dictionary for the CKAN resource.

[jqnatividad]

For an extended discussion about the data dictionary format, see DOI-DO/dcat-us#138